The present invention relates to a catalyst system for use in the preparation of substantially terminally unsaturated polyolefins.
Substantially terminally unsaturated polyolefins where the terminal group in the polymer is a vinylidene group have been used as starting materials for the preparation of a variety of compounds for example oil additives, sealants, dispersants, cleaning agents, etc. Such terminally unsaturated polyolefins, especially poly(iso)butenes, have been prepared using various catalysts such as boron trifluoride as claimed and described in our EP-A-0145235 and EP-A-0671419. Other processes have been used to produce conventional polymers of 1-olefins using catalysts such as metallocenes alone or in combination with an activator/cocatalyst such as methylaluminoxane. Polyolefins which can be produced by the latter method include homopolymers of propylene, 1-butene, 1-pentene, 1-hexene and 1-octene as well as copolymers of such olefins with one another, in particular copolymers of propylene e.g. with ethylene. Such polyolefins are characterised by a low molecular weight typically in the range 300-5000.
A particular advantage of such terminally unsaturated polymers is their high degree of reactivity especially towards enophiles such as unsaturated dicarboxylic acid anhydrides which make them particularly suitable for the ene/enophile reactions which enable functionalisation of such polymers into useful products such as lubricating oil additives.
For example EP-A-353935 describes ethylene/alpha-olefin copolymer substituted mono- and dicarboxylic acid lubricant dispersant additives in which the ethylene copolymer is prepared by use of bis(n-butylcyclopentadienyl)zirconium dichloride catalyst and methylaluminoxane (MAO) cocatalyst.
EP-A-490454 describes alkenyl succinimides as lube oil additives comprising an alkenyl substituent group derived from a propylene oligomer which is conveniently prepared using as a catalyst a bis(cyclopentadienyl)zirconium compound and cocatalyst MAO.
Similarly, EP-A-268214 describes the use of an alkyl substituted cyclopentadienyl compound of zirconium or hafnium for the oligomerisation of propylene. A vast number of compounds are listed which include inter alia [(CH3)5C5]2 ZrCl2. However, all the compounds listed are bis(penta-alkyl substituted cyclopentadiene) derivatives of zirconium or hafnium and these tend to give rise to polymers in which the terminal unsaturated linkage is predominantly a vinyl linkage.
EP 427697 describes a catalyst system based on a neutral metallocene, an aluminium alkyl and a Lewis acid e.g. tris(pentafluorophenyl)boron. In such a system the Lewis acid is utilised to ionize the neutral metallocene to form an ionic metallocene catalyst system. EP 570982 describes the use of a catalyst system comprising a metallocene, an organoaluminium compound and an ionic compound e.g. a trialkylammnonium borate. The catalyst system described may also comprise a boron compound e.g. tris(pentafluorophenyl) borane. Again in this system an ionic metallocene is prepared by interaction between the complex and the ionic compound.
We have now found that certain metallocene complexes when used in the presence of Group III metal alkyl compounds and Lewis acids comprising aryl boron compounds may be suitable for the preparation of substantially terminally unsaturated polyolefins having molecular weights in the range 300-500,000.
Thus according to the present invention there is provided a catalyst system suitable for use for the preparation of substantially terminally unsaturated atactic polymers or copolymers of xcex1-olefins having a number average molecular weight in the range 300-500,000 said catalyst system comprising (A) a metallocene of formula:
[RmCpH(5xe2x88x92m)][RnCpH(5xe2x88x92n)]M(Z)Y
wherein
CpH is a cyclopentadienyl ligand,
Each R represents an alkyl or an aryl substituent on the CpH ligand or two R groups may be joined together to form a ring, or the R groups in each CpH group when taken together represents an Si or C bridging group linking two CpH groups wherein
said Si or C group may itself be substituted by hydrogen atoms or C1-C3 alkyl groups,
M is a metal selected from hafnium, zirconium and titanium,
Z and Y are anionic ligands and may be the same or different, and
(B) a cocatalyst comprising (i) a Group III metal alkyl compound and (ii) a triarylboron compound.
Unless otherwise specified, the terms (co) polymers and (co) polymerisation are used herein and throughout the specification to cover the homopolymerisation and copolymerisation of xcex1-olefins as well as including oligomerisation.
By substantially terminally unsaturated polymers or copolymers is meant polymers or copolymers having xe2x89xa760% polymer chains which contain terminal unsaturation.
More specifically, catalysts that may be used to (co)polymerise xcex1-olefins include bis(alkyl cyclopentadienyl)metallocenes wherein R is a suitably a methyl group. Thus, the alkyl substituent on the cyclopentadienyl ligands in the metallocene may be a methyl-; 1,3-dimethyl-; 1,2,4-trimethyl-; or tetramethyl-group. Where R represents a substituted or unsubstituted silicon or carbon bridging group linking two CpH ligands, such metallocenes are suitably dimethylsilyl dicyclopentadienyl-zirconium, -hafnium or -titanium compound.
When two R groups are joined together the cyclopentadienyl ligand may be represented by indenyl or hydrogenated indenyl.
The metal M in the metallocene may be zirconium, hafnium or titanium. Of these zirconium is preferred.
The group Z or Y in the metallocene is preferably hydrocarbyl and most preferably alkyl. The most preferred metallocene complexes are those wherein Z and Y is methyl.
The preferred metallocenes for use in the present invention are bis(1,3-dimethylcyclopentadienyl)zirconium dimethyl and bis(cyclopentadienyl)zirconium dimethyl.
The Z and Y ligands may also be selected from a 1,3-diketone group, a xcex2-ketoester and a triflate. The diketonate comprises an anion of the formula
[R1xe2x80x94C(O)xe2x80x94C(R2)xe2x80x94C(O)xe2x80x94R3]xe2x88x92
where R1, R2 and R3 may be the same or different alkyl or aryl groups or halogenated alkyl groups and in addition R2 may be a hydrogen atom. The keto-ester anion comprises anions of the formula
xe2x80x83[R1xe2x80x94C(O)xe2x80x94C(R2)xe2x80x94C(O)xe2x80x94OR3]xe2x88x92
where R1, R2 and R3 may be the same or different alkyl or aryl groups or halogenated all groups and in addition R2 may be a hydrogen atom.
Of these, preferred metallocene catalysts which carry a methyl or a 1,3-dimethyl or a 1,2,4-trimethyl cyclopentadienyl ligands (ie when n is 1-3) give rise to (co)polymers in which the terminal unsaturation is predominantly a vinylidene group e.g. suitably  greater than 97%, preferably  greater than 99% vinylidene. However, where the value of each of m and n in these catalysts is 4 or 5, the product may comprise a significant proportion of vinyl terminated chains.
The cocatalyst comprises a Group III metal alkyl and a triarylboron compound.
Preferred Group III metal alkyl compounds are trialkylaluminium compounds in particular triisobutylalurninium. Other suitable Group III metal compounds include tri(sec-butyl)boron and triethyl boron.
A preferred triaryl boron compound is tris(pentatluorophenyl)boron.
In the catalyst system of the present invention the mole ratio of the triaryl boron to metallocene is suitably in the range 0.1 to 100, preferably in the range 0.5 to 50 and most preferably in the range 1 to 5.
The concentration of the Group III metal alkyl may be most beneficial between at a minimum that is required to neutralise any harmful impurities present in the feedstock and a maximum governed level by its potential to degrade the activating effect of the aryl boron compound.
Within the above range the mole ratio of the Group III metal alkyl to the aryl boron compound is in the range from 0.01 to 300, preferably in the range 0.5 to 100 and most preferably in the range 1 to 40.
The metallocene catalyst and the cocatalyst may suitably be supported on supports which include organic and inorganic materials such as polymers and inorganic metal and non-metal oxides, in particularly porous materials. While conventional support materials may be suitable, supports with particularly high porosity are preferred due to their ability to facilitate maximum contact between the reactants and catalyst while retaining the catalyst in supported form.
Examples of suitable support materials are macroporous or mesoporous silica or other non-metal or metal-oxides such as alumina, titania or mixtures of oxides. Alternatively the support may be a polymer. A preferred support is silica.
An important feature of the present invention is that these catalysts, when used to catalyse the (co)polymerisation of xcex1-olefins, give a product which is substantially pure in the sense that they only contain terminal unsaturation and is substantially free of any product which carries internal unsaturation.
The xcex1-olefins to be (co)polymerised suitably have 3 to 25 carbon atoms, preferably 3-12 carbon atoms which may be copolymerised with ethylene. Preferred xcex1-olefins are propylene, 1-butene or 1-decene. The reactant xcex1-olefin may be essentially pure xcex1-olefins or mixtures of xcex1-olefins with ethylene or dienes such as 1,7-octadiene, or, with inert diluents such as saturated hydrocarbons and halogenated solvents and/or minor amounts of other olefins. Preferred saturated hydrocarbon diluents are C4 hydrocarbons.
The catalysts of the present invention are particularly suitable for use in continuous liquid phase or in continuous fixed bed (co)polymerisation processes.
By using a fixed bed of the supported catalyst easy separation of catalyst and product may be achieved allowing isolation of a product containing very low catalyst residues beneficial for both the further functionalisation of the product as well as ensuring effective use of the catalyst system in a continuous process.
Catalyst separation may also be facilitated in a continuous liquid phase process by judicious selection of catalyst particle size which would allow easy physical separation of catalyst from product.
Operation of a continuous fixed bed process also allows control of residence time by controlling the feed rate. This may allow fine control of product molecular weight in addition to the usual method of temperature variation. For instance, for a given zirconocene catalyst according to the present invention, increasing the reaction temperature is likely to decrease the molecular weight of the (co)polymer product whereas increasing the monomer concentration is likely to increase the molecular weight of the polymer. Whichever technique is used, the polymers made using the catalysts of the present invention have a low molecular weight distribution, ie Mw/Mn=1.5 to 3, wherein Mw represent the weight average molecular weight and Mn represents the number average molecular weight of the (co)polymer.
Thus, according to a further embodiment, the present invention is a process for the preparation of substantially pure terminally-unsaturated polymers or copolymers of xcex1-olefins, said process comprising polymerising or co-polymerising the xcex1-olefin(s) in the presence of a catalyst system as hereinbefore described.
The (co)polymerisation reaction is suitably carried out in the liquid/vapour phase. Where it is carried out in the liquid phase, it is preferable that the reactants and catalysts are dissolved in a diluent which may be a saturated/unsaturated or aromatic hydrocarbon or a halogenated hydrocarbon which is/are normally inert under the reaction conditions and which do not interfere with the desired (co)polymerisation reaction. Examples of suitable solvents that may be used include inter alia toluene, xylene, isobutane, propane, hexane, etc. It is important that the reactants, catalysts and solvents, if any, used are pure and dry and contain no polar groups or contaminants.
The (co)polyrnerisation reaction is suitably carried out at a temperature in the range from 20 to 150xc2x0 C., preferably in the range from 50 to 100xc2x0 C. If it is desired to vary the molecular weight of a product (co)polymer for a given catalyst this variationxe2x80x94whilst difficultxe2x80x94is conventionally achieved by a significant change in the reaction conditions. For instance, more dilution may be needed or the reaction may have to be run at higher temperatures to achieve a product of relatively lower molecular weight. Raising the temperature within this range is not favoured since this may lead to xcex1-olefin mis-insertion into the growing (co)polymer chain thereby leading to earlier termination and to the formation of less favoured internal olefin functionality in the (co)polymer. However, using the novel metallocene catalyst systems of the present invention, the molecular weight may be more easily controlled/varied by change of the nature of the leaving groups for a given catalyst system without sacrificing the benefit of high vinylidene content in the product (co)polymer.
The terminally unsaturated polymers of the present invention can be used either directly or be readily further derivatised using the high terminal unsaturation to make products suitable for use as fuel and lubricant additives such as dispersants, wax modifiers, flow improvers, dispersant-viscosity index improvers, viscosity modifiers and the like. The molecular weight of the polymers prepared according to the present invention are tailored according to the application required. For example Mn is maintained in the range from about 300 to about 10,000 for dispersant applications and from about 15,000 to about 500,000 for viscosity modifier applications. Where the polymer is required to have some dispersancy performance it is necessary to introduce polar functionality which enables the molecule to bind well to engine deposits and sludge forming materials.
Thus according to another aspect of the present invention there is provided a method of controlling the molecular weight of substantially terminally unsaturated atactic polymers or copolymers of xcex1-olefins having a molecular weight in the range 300-500,000 by use of a catalyst system as hereinbefore described.
The reaction is suitably carried out in pressure range 10-40 bar but can be carried out at lower or higher pressures. The duration of the reaction is suitably in the range from 1 to 20 hours, preferably from 1 to 10 hours, and is usually from 1 to 3 hours.
The reaction when complete is terminated by venting the reactor and reducing the reaction temperature to about 20xc2x0 C. A lower alcohol such as isopropanol can be added to the reactor after venting in order to quench the catalyst. The resulting (co)polymer which is in solution in the reaction solvent such as e.g. toluene is then drained from the base of the reactor and the reactor then washed with the reaction solvent. A solution of the reaction product in the reaction solvent is then washed with a small amount of dilute acid, e.g. hydrochloric acid, and then with distilled water, dried with magnesium sulphate, filtered and the reaction solvent removed by evaporation on a rotary evaporator. The evaporation is suitably carried out at 120 mbar pressure (although higher vacuums can be used) at 85xc2x0 C. for about 3 hours and the oligomer/polymer is then recovered as residue.
A further feature of the present process is that the (co)polymers thus formed have a relatively low level of catalyst, cocatalyst or support residues when compared with (co)polymers obtained by (co)polymerisation using conventional catalyst/cocatalyst processes whether in slurry or dissolved form.
Furthermore the catalyst and reaction conditions are controlled such that the process produces essentially non crystalline (co) polymers. Absence of crystallinity is desirable to prevent the formation of cloudy and/or aggregated solutions. For polymers of xcex1-olefins it is necessary to ensure that the polymers are atactic. When ethylene is used as a comonomer, it is important to control the ethylene concentration and distribution in the copolymer such that there are insufficient run lengths of ethylene segments present to give rise to crystallinity. For this reason it is necessary to limit the mole fraction of ethylene present in the (co) oligomer to less than 70 mole %, preferably less than 50 mole % and to ensure that the monomer feed ratio is well controlled throughout the reaction.
According to another aspect of the present invention there are provided substantially terminally unsaturated atatic polymers or copolymers of xcex1-olefins having molecular weight in the range 300-500,000 prepared using a catalyst system as hereinbefore described.